Multilayer composite comprising layers of partly aromatic polyamides

ABSTRACT

A multilayer composite containing the following layers: 1. a first layer (layer I) of a moulding compound containing at least 40 wt. % of the following components: 1) 60 to 99 parts by wt. of a copolyamide based on hexamethylenediamine, terephthalic acid and an aliphatic dicarboxylic acid having 8 to 19 carbon atoms and 2) 40 to 1 parts by wt. of an olefinic copolymer as impact modifier, wherein the parts by wt. of 1) and 2) sum to 100; and II. a second layer (layer II) of a moulding compound containing at least 60 wt. % of a mixture of the following components: 1) 75 to 100 parts by wt. of a partly aromatic copolyamide and 2) 25 to 0 parts by wt. of an olefinic copolymer as impact modifier with the proviso that in the moulding compound of layer II the mixture of components 1) and 2) comprises at least 5 fewer parts by wt, of olefinic copolymer than in the moulding compound of layer I, has a high heat distortion temperature, a very good impact resistance, a high elongation at break and good layer adhesion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer composite comprising a barrier layer of a partly aromatic polyamide and a layer of a moulding compound based on an impact-modified partly aromatic polyamide. The multilayer composite is primarily a hollow article, for instance a hollow profile or a container for conducting or storing liquid or gaseous media.

2. Discussion of the Background

The development of multilayer composites employed, for example, as pipes for conducting liquid or gaseous media in motor vehicles is subject to automotive industry demands for an improved barrier effect, for fuel lines in particular, to reduce emissions of fuel components into the environment as well as to requirements of sufficient fuel resistance. This has resulted in the development of multilayer pipe systems where, for example, fluoropolymers, ethylene vinyl alcohol copolymers (EVOH) or thermoplastic polyesters are employed as the barrier layer material. Additionally, WO 2005/018891 discloses hollow articles comprising at least one layer of an impact-modified partly aromatic polyamide and optionally one or more layers of aliphatic polyamide,

Multilayer composites composed of two different layers which are both based on a polyamide composed of an aromatic dicarboxylic acid and an aliphatic diamine having 9 to 13 carbon atoms, wherein the layer materials comprise different amounts of impact modifiers, are known from EP 1 864 796 A1 and JP 2009-119682 A. However in this solution the monomer basis on the diamine side is relatively costly. Such polyamides can moreover be processed only with difficulty which is manifested, for example, in insufficient dimensional accuracy during layer construction. A further disadvantage of these multilayer composites is their low elongation at break. For automotive applications a high elongation at break is required, so that in the event of an accident the fuel lines or similar lines remain undamaged. Thus, a pipe having a 800 μm—thick layer of an impact-modified PA9T and a 200 μm—thick layer of an ETFE is produced in comparative example 24 of US 2014/0299220 A1; the elongation at break here is 22%, However, in such pipes an elongation at break of more than 100% is desirable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide, with moulding compounds which have better processability and can be produced economically, a composite which comprises a barrier layer based on a partly aromatic polyamide and an impact- modified polyamide layer and has a high heat distortion temperature, a high impact resistance and a high elongation at break and moreover exhibits good layer adhesion. The invention should moreover provide the opportunity to employ an inner layer material where only a very small amount of oligomers is washed out and there are accordingly no blockages in the fuel supply to the engine.

The present invention relates to a multilayer composite, comprising the following layers:

-   -   I. a first layer (layer I) of a moulding compound comprising at         least 40 wt. % of the following components:         -   1) 60 to 95 parts by wt. of a partially aromatic copolyamide             which contains monomer units which are obtained from             -   α) 30 to 90 mol % of a combination of                 hexamethylenediamine and terephthalic acid, and             -   β) 70 to 10 mol % of a combination of                 hexamethylenediamine and a linear aliphatic dicarboxylic                 acid having 8 to 19 carbon atoms;             -   wherein the mol % values relate to the sum of α) and β),                 and             -   wherein not more than 20% of the hexamethylenediamine is                 optionally replaced by the equivalent amount of another                 diamine, and/or             -   wherein not more than 20% of the terephthalic acid is                 optionally replaced by the equivalent amount of another                 aromatic dicarboxylic acid and/or                 1,4-cyclohexanedicarboxylic acid, and/or             -   wherein not more than 20% of the repeating units                 containing hexamethylenediamine and linear aliphatic                 dicarboxylic acid is optionally replaced by the                 equivalent quantity of units obtained from a lactam/an                 ω-aminocarboxylic acid having 6 to 12 carbon atoms,         -   2) 40 to 5 parts by wt. of an olefinic copolymer as impact             modifier, wherein the parts by wt. of 1) and 2) sum to 100;             and     -   II. a second layer (layer II) of a moulding compound comprising         at least 60 wt. % of a mixture of the following components:         -   -   1) 75 to 100 parts by wt, of a partly aromatic                 copolyamide, and             -   2) 25 to 0 parts by wt. of an olefinic copolymer as                 impact modifier with the proviso that in the moulding                 compound of layer II the mixture of components 1) and 2)                 comprises at least 5 fewer parts by wt. of olefinic                 copolymer than in the moulding compound of layer I,

DETAILED DESCRIPTION OF THE INVENTION

The ranges below include all values and subvalues between the lower and higher limit of the range.

The present invention relates to a multilayer composite comprising the following layers:

-   -   I. a first layer (layer I) of a moulding compound comprising at         least 40 wt. %, preferably at least 50 wt. %, particularly         preferably at least 60 wt. %, especially preferably at least 70         wt. % and very particularly preferably at least 80 wt. % of a         mixture of the following components:         -   1) 60 to 95 parts by wt., preferably 65 to 92 parts by wt.,             particularly preferably 68 to 90 parts by wt. and especially             preferably 70 to 88 parts by wt. of a partly aromatic             copolyamide consisting of monomer units obtained from             -   α) 30 to 90 mol %, preferably 35 to 85 mol %,                 particularly preferably 40 to 80 mol %, especially                 preferably 41 to 75 mol % and very particularly                 preferably 45 to 70 mol % of a combination of                 hexamethylenediamine and terephthalic acid and             -   β) 70 to 10 mol %, preferably 65 to 15 mol %,                 particularly preferably 60 to 20 mol %, especially                 preferably 59 to 25 mol % and very particularly                 preferably 55 to 30 mol % of a combination of                 hexamethylenediamine and a linear aliphatic dicarboxylic                 acid having 8 to 19 carbon atoms,             -   wherein the mol % values relate to the sum of α) and β)                 and wherein not more than 20%, preferably not more than                 15%, particularly preferably not more than 12%,                 especially preferably not more than 8% and very                 particularly preferably not more than 5% or not more                 than 4% of the hexamethylenediamine may be replaced by                 the equivalent amount of another diamine and/or wherein                 not more than 20%, preferably not more than 15%,                 particularly preferably not more than 12%, especially                 preferably not more than 8% and very particularly                 preferably not more than 5% or not more than 4% of the                 terephthalic acid may be replaced by the equivalent                 amount of another aromatic dicarboxylic acid and/or                 1,4-cyclohexanedicarboxylic acid and/or wherein not more                 than 20%, preferably not more than 15%, particularly                 preferably not more than 12%, especially preferably not                 more than 8% and very particularly preferably not more                 than 5% or not more than 4% of the repeating units                 composed of hexamethylenediamine and linear aliphatic                 dicarboxylic acid may be replaced by the equivalent                 quantity of units obtained from a lactam/an                 ω-aminocarboxylic acid having 6 to 12 carbon atoms,         -   2) 40 to 5 parts by wt., preferably 35 to 8 parts by wt.,             particularly preferably 32 to 10 parts by -wt. and             especially preferably 30 to 12 parts by wt. of an olefinic             copolymer as impact modifier,     -   wherein the parts by wt. of 1) and 2) sum to 100; and     -   II. a second layer (layer II) of a moulding compound comprising         at least 60 wt. %, preferably at least 70 wt. %, particularly         preferably at least 80 wt. %, especially preferably at least 90         wt. % and very particularly preferably at least 95 wt. % of a         mixture of the following components:         -   1) 75 to 100 parts by wt., preferably 80 to 99 parts by wt.,             particularly preferably 83 to 98 parts by wt. and especially             preferably 85 to 97 parts by wt. of a partly aromatic             copolyamide and         -   2) 25 to 0 parts by wt., preferably 20 to 1 parts by wt.,             particularly preferably 17 to 2 parts by wt. and especially             preferably 15 to 3 parts by wt. of an olefinic copolymer as             impact modifier     -   with the proviso that in the moulding compound of layer II the         mixture of components 1) and 2) comprises at least 5 fewer parts         by wt., preferably at least 8 fewer parts by wt., particularly         preferably at least 12 fewer parts by wt, and very particularly         preferably at least 15 fewer parts by wt. of olefinic copolymer         than in the moulding compound of layer I.

In a particularly preferred embodiment the sum of the components 1) and 2) in layer II comprises 0 to 10 parts by wt. of the impact modifier, very particularly preferably 0 to 5 parts by wt. and especially preferably no impact modifier.

Suitable for employment as the linear aliphatic dicarboxylic acid having 8 to 19 carbon atoms are: ocianedioic acid (suberic acid; C₈), nonanedioic acid (azelaic acid; C₉), decanedioic acid (sebacic acid; C₁₀), undecanedioic acid (C₁₁), dodecanedioic acid (C₁₂), tridecanedioic acid (C₁₃), tetradecanedthic acid (C₁₄), pentadecanedioic acid (C₁₅), hexadecanedioic acid (C₁₆), heptadecanedioic acid (C₁₇), octadecanedioic acid (C₁₈) and nonadecanedioic acid (C₁₉).

In accordance with the claims a portion of the hexamethylenediamine may optionally be replaced by another diamine. Any diamine is suitable here in principle and the following diamines may be cited by way of example: 1,10-decanediamine, 1,12-dodecanediamine, m-xylylenediamine, p-xylylenediamine, bis(4-aminocyclohexyl)methane, 2-methyl-1,5-pentanediamine and 1,4-bis-aminomethylcyclohexane. It will be appreciated that it is also possible to employ mixtures of such diamines. However, it is preferable when no further diamine is employed in addition to hexamethylenediamine.

In accordance with the claims a portion of the terephthalic acid may also optionally be replaced by another aromatic dicarboxylic acid or by 1,4-cyclohexanedicarboxylic acid. Any aromatic dicarboxylic acid is suitable here in principle and the following dicarboxylic acids may be cited by way of example: isophthalic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyl ether dicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid and 1,5-naphthalenedicarboxylic acid. It will be appreciated that it is also possible to employ mixtures of such dicarboxylic acids. However, it is preferable when no further aromatic dicarboxylic acid and/or no 1,4-cyclohexanedicarboxylic acid is employed in addition to terephthalic acid. Similarly, in accordance with the claims a portion of the repeating units composed of hexamethylenediamine and linear aliphatic dicarboxylic acid may optionally be replaced by a lactam/an co-aminocarboxylic acid having 6 to 12 carbon atoms. Here, the repeating unit composed of hexamethylenediamine and linear aliphatic dicarboxylic acid corresponds to a unit derived from a lactam/an ω-aminocarboxylic acid. Examples of lactams/ω-aminocarboxylic acids having 6 to 12 carbon atoms include caprolactam, capryl lactam, undecanolactam, ω-aminoundecanoic acid, lauryl lactam and ω-aminododecanoic acid. Preference is given here to lactams/an ω-aminocarboxylic acids having 11 or 12 carbon atoms. However, it is preferable when no lactam/no ω-aminocarboxylic acid is employed in addition to hexamethylenediamine and linear aliphatic dicarboxylic acid.

The composition of the partially aromatic copolyamide is advantageously selected such that its crystallite melting point T_(m) as per ISO 11357 and measured at 2nd heating is in the range from 220° C. to 300° C., preferably in the range from 230° C. to 295° C. and particularly preferably in the range from 240° C. to 290° C. When there are several melting peaks T_(m) is determined from the main melting peak.

The copolyamide is generally produced by melt polycondensation. Appropriate methods are related art. It is alternatively possible to employ any other known method of polyamide synthesis.

A necessarily equimolar combination of hexamethylenediamine and terephthalic acid is provided when it is ensured that these monomers can react in a molar ratio of 1:1. It may be noted that hexamethylenediamine is relatively volatile and that losses may therefore occur during the polycondensation which need to be compensated with a larger charge. It may moreover be necessary to deviate slightly from the exact stoichiometry to establish a particular end group ratio. The same applies to 1)β) for the necessarily equimolar combination of hexamethylenediamine and a linear aliphatic dicarboxylic acid having 8 to 19 carbon atoms.

In a preferred embodiment the partly aromatic polyamide has a ratio of amino end groups to the sum of amino and carboxyl end groups of 0.3 to 0.7 and particularly preferably 0.35 to 0.65. The fraction of amino end groups may be adjusted by controlling the polycondensation using methods known to those skilled in the art. Control may be effected by varying the ratio of diamine employed to dicarboxylic acid employed, by addition of a monocarboxylic acid or by addition of a monoamine. The fraction of amino end groups may also be adjusted by mixing two copolyamides, of which one is rich in amino end groups and the other is low in amino end groups, as pellets or as a melt.

The amino group content may be determined by titration of a solution of the copolyamide in m-cresol using perchloric acid. The determination of the carboxyl group content may be effected by titration of a solution of the copolyamide in o-cresol using KOH in ethanol. These methods are familiar to those skilled in the art.

The impact modifier is in particular an olefinic copolymer comprising units of the following monomers:

-   -   a) 20 to 99.9 wt. % and preferably 30 to 99.7 wt. % of one or         more α-olefins having 2 to 12 carbon atoms,     -   b) 0 to 50 wt. % of one or more acrylic compounds selected from         -   acrylic acid, methacrylic acid and salts thereof and         -   esters of acrylic acid/methacrylic acid with a C₁ to C₁₂             alcohol, with the exception of epoxy group-containing esters             such as glycidyl acrylate and glycidyl methacrylate,     -   c) 0.1 to 50 wt. % of an olefinically unsaturated epoxide or         dicarboxylic anhydride,     -   wherein the wt. % values relate to the olefinic copolymer and         sum to not more than 100. It should be noted that units derived         from further comonomers, for example from styrene or an         unconjugated diene, may additionally be present.

When the component c) is composed of units derived from an unsaturated dicarboxylic anhydride, said units are preferably present in amounts of 0.1 to 8 wt. %, particularly preferably 0.3 to 5 wt. %.

When the component c) is composed of units derived from an olefinically unsaturated epoxide, the acrylic compound according to b) comprises neither acrylic acid nor methacrylic acid.

In a first embodiment the impact modifier is an olefinic copolymer comprising the following monomer units:

-   -   35 to 94.9 wt. %, preferably 40 to 90 wt. % and particularly         preferably 45 to 85 wt. % of monomer units based on ethene,     -   5 to 65 wt. %, preferably 10 to 60 wt. % and particularly         preferably 15 to 55 wt. % of monomer units based on a 1-alkene         having 4 to 8 carbon atoms,     -   0 to 10 wt. % of monomer units based on another olefin and     -   0A to 2.5 wt. % of monomer units based on an aliphatically         unsaturated dicarboxylic anhydride,     -   wherein the individual fractions are chosen such that these wt.         % values sum to 100.

Further inventive lower limits for the monomer units based on ethane are 34.9 wt. %, preferably 39.9 wt. % and particularly preferably 44.9 wt. %, while further inventive upper limits therefor are preferably 89.9 wt. % and particularly preferably 84.9 wt. %.

Suitable for employment in the olefinic copolymer as the 1-alkene having 4 to 8 carbon atoms are the following compounds: 1-butene, 1-pentene, 1-hexene, 1-heptene and 1-octene. It will be appreciated that the monomer units based on a 1-alkene having 4 to 8 carbon atoms may also be derived from mixtures of these compounds.

There is no restriction on the nature of the other olefin whose monomer units can make up from 0 to 10 wt. % of the olefinic copolymer. For example said olefin may be an unconjugated diene, a mono-ene such as propene, 4-methyl-1 -pentene or styrene or a mixture thereof.

In a first variant the other olefin whose monomer units can make up from 0 to 10 wt. % of the olefinic copolymer is not an unconjugated diene.

In a second variant this other olefin is not styrene and/or not propene.

In a third variant the olefinic copolymer comprises only monomer units derived from ethene, a 1-alkene having 4 to 8 carbon atoms and an aliphatically unsaturated dicarboxylic anhydride.

In a fourth variant the 1-alkene having 4 to 8 carbon atoms is 1-butene.

In a fifth variant the 1-alkene having 4 to 8 carbon atoms is 1-hexene.

In a sixth variant the 1-alkene having 4 to 8 carbon atoms is 1-octene.

These variants may be combined with one another without restriction.

The aliphatically unsaturated dicarboxylic anhydride may be, for example, maleic anhydride but other corresponding compounds such as aconitic anhydride, citraconic anhydride or itaconic anhydride for instance are also suitable.

The olefinic copolymer according to the claims may be produced in known fashion, wherein the aliphatically unsaturated dicarboxylic anhydride or a precursor thereof, for example the corresponding acid or a half ester, is reacted with a preformed copolymer by thermal or preferably by free-radical reaction. Here the aliphatically unsaturated dicarboxylic anhydride may also be reacted in combination with other monomers, for example with dibutyl fumarate or styrene. Olefinic copolymers according to the claims are commercially available in various types,

In a second embodiment the impact modifier is an olefinic copolymer comprising the following monomer units:

-   -   35 to 94.9 wt. %, preferably 40 to 90 wt. % and particularly         preferably 45 to 85 wt. % of monomer units based on ethene,     -   5 to 65 wt. %, preferably 10 to 60 wt. % and particularly         preferably 15 to 55 wt. % of monomer units based on propene,     -   0 to 10 wt. % of monomer units based on another olefin, for         example an unconjuaated diene, and     -   0.1 to 2.5 wt. % of monomer units based on an aliphatically         unsaturated dicarboxylic anhydride,

wherein the individual fractions are chosen such that these wt. % values sum to 100.

Further inventive lower limits for the monomer units based on ethane are 34.9 wt. %, preferably 39.9 wt. % and particularly preferably 44.9 wt. %, while further inventive upper limits therefor are preferably 89.9 wt. % and particularly preferably 84.9 wt. %.

In the third embodiment the impact modifier is a hydrogenated and anhydride-modified block copolymer comprising at least one polyvinylaromatic block A and at least one polyolefin block B. The blocks may be arranged in linear or star-shaped fashion, for example as structures of the type A-B, A-B-A. B-A-B. A-B-A-B, A-B-A--B-A, B-A-B-A-B, (A)B₃, (B)A₃, (A)(B-A)₃, (B)(A-B)₃, wherein the number-average molecular weight of these block copolymer is in the range from about 10 000 to about 800 000 and preferably in the range from about 20 000 to about 500 000, The fraction of vinylaromatic compound in the block copolymer is preferably 10 to 70 wt. % and particularly preferably 10 to 55 wt. %. The rubber-like polyolefin blocks B comprise, for example, ethylene/propylene, ethyleneibutylene or ethylene/pentylene units; they are obtained by polymerization of conjugated dienes and, in particular, of butadiene isoprene, 1,3-pentadiene, 2,3-dimethylbutadiene or mixtures thereof and by subsequent selective hydrogenation. This hydrogenates at least 80% of the aliphatic double bonds in the polymerized diene fraction, preferably at least 90% and particularly preferably at least 94%. The vinylaromatic compound used to produce the polyvinylaromatic block is typically styrene but it is also possible to employ α-methylstyrene or the like. The hydrogenated block copolymer comprises 0.1 to 8 wt. % and preferably 0.3 to 5 wt. % of succinic anhydride groups which are introduced by reaction with an unsaturated dicarboxylic acid or anhydride thereof such as maleic anhydride, citraconic acid, itaconic acid or the like either before or preferably after the hydrogenation. The production of such anhydride-modified, hydrogenated vinylaromatic/conjugated diene block copolymers is related art; suitable types are commercially available, for example under the trade name Kraton® FG1901X. This is a linear triblock copolymer of the SEBS type (styrene-ethylene/butylene-styrene) having a polystyrene content of 30 wt. % and a content of succinic anhydride groups of 1.4 to 2 wt. %,

In a fourth embodiment the impact modifier is a mixture of

-   -   5 to 95 wt. % of an olefinic copolymer comprising units of the         following monomers:         -   a) 20 to 99.9 wt. % of one or more α-olefins having 2 to 12             carbon atoms,         -   b) 0 to 50 wt. % of esters of acrylic acid or methacrylic             acid with a C₁ to C₁₂ alcohol with the exception of epoxy             group-containing esters, and         -   c) 0.1 to 50 wt. % of an olefinically unsaturated epoxide,     -   wherein the wt. % values relate to the olefinic copolymer and         sum to not more than 100, and     -   95 to 5 wt. % of an olefinie copolymer comprising units of the         following monomers:         -   a) 42 to 99.9 wt % of one or more α-olefins having 2 to 12             carbon atoms,         -   b) 0 to 50 wt. % of esters of acrylic acid or methacrylie             acid with a C₁ to C₁₂ alcohol with the exception of epoxy             group-containing esters, and         -   c) 0.1 to 8 wt. % of an olefinically unsaturated             dicarboxylic anhydride, wherein the wt. % values relate to             the olefinic copolymer and sum to not more than 100.

The α-olefin having 2 to 12 carbon atoms is, for example, selected from ethene, propene, 1-butene, 1-pentene, 4-methylpera-1-ene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene and 1-dodecene, preference being given to ethene,

Examples of esters of acrylic acid or methacrylic acid include, in particular, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate and 2-ethylhexyl methacrylate.

Examples of olefinically unsaturated epoxides include, in particular, glycidyl esters and glycidyl others, such as glycidyl acrylate, glycidyl methacrylate, glycidyl maleate, glycidyl itaconate, vinylglycidyl ether and allylglycidyl ether.

Examples of olefinically unsaturated dicarboxylic anhydrides include maleic anhydride, itaconic anhydride, citraconic anhydride, 2,3-dimethylmaleic anhydride and bicyclo[2.2.2]oct-5-ene-2,3-dicarboxylic anhydride.

In a fifth embodiment the impact modifier is a mixture of

-   -   70 to 99 wt. %, of the impact modifier from the first embodiment         and     -   1 to 30 wt. % of an olefinic copolymer comprising units of the         following monomers:         -   a) 20 to 99.9 wt. % of one or more α-olefins having 2 to 12             carbon atoms,         -   b) 0 to 50 wt. % of esters of acrylic acid or methacrylic             acid with a C₁ to C₁₂ alcohol with the exception of epoxy             group-containing esters, and         -   c) 0.1 to 50 wt. % of an olefinically unsaturated epoxide,         -   wherein the wt. % values relate to the olefinic copolymer             and sum to not more than 100.

The details of the olefinic copolymer employed here are the same as described for the fourth embodiment.

In a sixth embodiment the impact modifier is a mixture of

-   -   70 to 99 wt. % of the impact modifier from the second embodiment         and.     -   1 to 30 wt. % of an olefinic copolymer comprising units of the         following monomers:         -   a) 20 to 99.9 wt. % of one or more α-olefins having 2 to 12             carbon atoms,         -   b) 0 to 50 wt. % of esters of acrylic acid or methacrylic             acid with a C₁ to C₁₂ alcohol with the exception of epoxy             group-containing esters, and         -   c) 0.1 to 50 wt. % of an olefinically unsaturated epoxide,         -   wherein the wt. % values relate to the olefinic copolymer             and sum to not more than 100.

The details of the copolymer employed here are the same as described for the fourth embodiment.

In a seventh embodiment the impact modifier is a tune of

-   -   50 to 99 wt. % of the impact modifier from the first embodiment         and     -   1 to 50 wt. % of the hydrogenated and anhydride-modified block         copolymer from the third embodiment,

In an eighth embodiment the impact modifier is a mixture of

-   -   50 to 99 wt. % of the impact modifier from the second embodiment         and.     -   1 to 50 wt. % of the hydrogenated and anhydride-modified block         copolymer from the third embodiment.

These embodiments are merely exemplary. It is also possible in the context of the invention to employ other impact modifiers not cited here. The first embodiment is particularly preferred here since such moulding compounds have a particularly high thermal ageing resistance. Also preferable are the fifth and the seventh embodiment which likewise comprise the impact modifier from the first embodiment.

In addition to the components 1) and 2) the moulding compound of layer fused according to the invention optionally contains further additions which make up the balance to 100 wt. %, and preferably at least 0.1 wt. % thereof. Examples of se further additions include:

-   -   a) stabilizers,     -   b) other polymers,     -   c) plasticizers,     -   d) pigments and/or dyes,     -   e) additions which increase electrical conductivity and     -   f) processing aids.

In a preferred embodiment, the moulding compound contains an active amount of a copper-containing stabilizer. This is in particular a copper compound soluble in the poly-amide matrix. The copper compound is preferably combined with an alkali metal halide.

In certain embodiments, the stabilizer is a copper(I) salt, e.g., copper acetate, copper stearate, an organic copper complex, for example copper acetylacetonate, a copper halide or the like in combination with an alkali metal halide.

In certain embodiments, the copper-containing stabilizer comprises a copper halide selected from copper iodide and copper bromide and an alkali metal halide selected from the iodides and bromides of lithium, sodium and potassium.

It is preferable to employ the copper-containing stabilizer in an amount such that the moulding compound contains 20 to 2000 ppm of copper, particularly preferably 30 to 1500 ppm of copper and especially preferably 40 to 1000 ppm of copper.

It is further preferable when the copper-containing stabilizer has a composition such that the weight ratio of alkali metal halide to copper compound is in the range from 2.5 to 12 and particularly preferably in the range from 6 to 10. The combination of alkali metal halide and copper compound is generally present in the moulding compound in an amount of from about 0.01 wt. % to about 2.5 wt. %.

The copper-containing stabilizer offers protection against long-term thermal ageing, for example in under-bonnet automobile applications,

In a further preferred embodiment, the moulding compound comprises an active amount of an oxidation stabilizer and particularly preferably an active amount of an oxidation stabilizer in combination with the active amount of a copper-containing stabilizer. Examples of suitable oxidation stabilizers include aromatic amines, sterically hindered phenols, phosphites, phosphonites, thio synergists, hydroxylamines, benzofuranone derivatives, acryloyl-modified phenols etc. A great many types of such oxidation stabilizers are commercially available, for example under the trade names Naugard 445, Irganox 1010, Irganox 1098, Irgafos 168, P-EPQ or Lowinox DSTDP. The moulding compound generally comprises about 0.01 to about 2 wt. % and preferably about 0.1 to about 1.5 wt. % of an oxidation stabilizer.

The moulding compound may moreover further comprise a UV stabilizer/a light stabilizer of the HALS type. Suitable UV stabilizers are primarily organic IN absorbers, for example benzophenone derivatives, benzotriazole derivatives, oxalanilides or phenyltriazines. Light stabilizers of the HALS type are tetramethylpiperidine derivatives; these are inhibitors which act as radical scavengers. UV stabilizers and light stabilizers may advantageously be used in combination. A great many types of both are commercially available; the manufacturer's instructions can be followed in respect of the amounts employed.

The moulding compound may additionally comprise a hydrolysis stabilizer, for instance a monomeric, oligomeric or polymeric carbodiimide or a bisoxazoline.

Examples of other polymers which may be present in the moulding compound as an addition include aliphatic polyamides, polyether amides, or polytetrafluoroethylene (PTFE).

Examples of suitable aliphatic polyamides include PA46, PA66, PA68, PA610, PA612, PA613, PA410, PA412, PA810, PA1010, PA1012, PA101.3, PA1014, PA1018, PA1212, PA6, PA11 and PA12 and also copolyamides derived from these types. It is preferable when the polyamide fraction of the moulding compound composed of the partially aromatic copolyamide, optionally aliphatic polyamide and optionally polyether amide comprises less than 10 wt. %, particularly preferably less than 8 wt. %, especially preferably less than 5 wt. % and very particularly preferably less than 3 wt. % of aliphatic polyamide or preferably less than 10 wt. %, particularly preferably less than 8 wt. %, especially preferably less than 5 wt. % and very particularly preferably less than 3 wt. % of the sum of aliphatic polyamide and polyether amide.

Plasticizers and the use thereof in polyamides are known, A general overview of plasticizers suitable for polyamides may be found in Gächter/Müller, Kunststoffadditive [Plastics additives], C. Hanser Verlag, 2nd edition, p 296.

Examples of conventional compounds suitable for employment as plasticizers include esters of p-hydroxybenzoic acid having 2 to 20 carbon atoms in the alcohol component or amides of arylsulfonic acids having from 2 to 12 carbon atoms in the amine component, preferably amides of benzenesulphonic acid.

Suitable plasticizers include, inter alia, ethyl p-hydroxybenzoate, octyl p-hydroxybenzoate, i-hexadecyl p-hydroxybenzoate, toluenesulphonic acid n-octylamide, benzenesulphonic acid n-butylamide or benzenesulphonic acid 2-ethylhexylamide.

Examples of suitable pigments and/or dyes include carbon black, iron oxide, zinc sulphide, ultramarine, nigrosin, pearlescent pigments and metal flakes.

Examples of additions which increase in electrical conductivity include conductivity carbon black or carbon nanotubes.

Examples of suitable processing aids include paraffins, fatty alcohols, fatty acid amides, stearates such as calcium stearate, paraffin waxes, montanates or polysiloxanes.

The moulding compound is produced from the individual constituents in a manner known to those skilled in the art by melt mixing.

The partly aromatic polyamide of layer II generally has the composition PAXY/Z, wherein the individual units have the following meanings:

X is a unit derived from an aromatic dicarboxylic acid;

Y is a unit derived from a diamine. The diamine is preferably linear aliphatic or branched aliphatic but may also be cycloaliphatic or aromatic;

Z is either a unit derived from a lactam or an ω-aminocarboxylic acid, or a unit derived from the combination of a linear aliphatic, branched aliphatic or cycloaliphatic dicarboxylic acid and a linear aliphatic, branched aliphatic or cycloaliphatic diamine.

Here, the proportion of Z based on the sum of X, Y and Z is 0 to 60 mol %, preferably 0 to 50 mol %, particularly preferably 1 to 40 mol %, especially preferably 2 to 30 mol % and very particularly preferably 4 to 20 mol %,

The aromatic dicarboxylic acid from which the unit X is derived may be, for example, terephthalic acid 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, isophthalic acid, biphenyl-4,4′-dicarboxylic acid, diphenyl ether-4,4′-dicarboxylic acid. or any other aromatic dicarboxylic acid. Preference is given to employing terephthalic acid or 2,6-naphthalenedicarboxylic acid.

The linear aliphatic diamine from which the unit Y may be derived and/or which, together with a dicarboxylic acid, can give the unit Z may be, for example, 1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine, 1,7-heptanediamine, 1,8-octanediamine, 1,9-nonanediamine, 1,10-decanediamine, 1,11-undecanediamine, 1,12-dodecanediamine, 1,13-tridecanediamine, 1,14-tetradecanediamine or 1,18-octadecanediamine.

The branched aliphatic diamine from which the unit Y may be derived and/or which, together with a dicarboxylic acid, may give the unit Z may be, for example, 2-methyl-1,5-pentanediamine, 2,2,4-trimethyl-1,6-hexanediamine, 2,4,4-trimethyl-1,6-hexanediamine, diethyl-1,6-hexanediamine, 2,2-dimethyl-1,7-heptanediamine, 2,3dimethyl-1,7-heptanediamine, 2,4-dimethyl-1,7-heptanediamine, 2,5-dimethyl-1,7-heptanediamine, 2-, 3- or 4-methyl-1,8-octanediamine, 1,3-, 1,4-, 2,2-4-, 3,3-, 3,4-, 4,4- or 4,5-dimethyl-1,8-octanediamine, 5-methyl-1,9-nonanediamine, 2-butyl-1,8-octanediamine or 3-butyl-1,8-octanediamine. It is also possible to employ mixtures thereof, for example the isomer mixtures obtained during production,

The cycloaliphatic diamine from which the unit Y may be derived and/or which, together with a dicarboxylic acid, may give the unit Z may be, for example, 1,3- or 1,4-cyclohexanediamine, 1,3- or 1,4-cyclohexanedimethylamine, bis(4-aminocyclohexyl)methane, bis(4-aminocyclohexyl)propane or isophoronediamine,

The aromatic diamine from which the unit Y may be derived may be, for example, p-phenylenediamine, m-phenylenediamine, p-xylylenediamine, m-xylylenediamine or 4,4′-diaminodiphenyl ether,

The lactam from which the unit Z may be derived is, for example, caprolactam or laurolactam.

The ω-aminocarboxylic acid from which the unit Z may be derived is, for example, ω-aminoundecanoic acid.

The linear aliphatic dicarboxylic acid which, together with a diamine, may give unit Z is, for example, adipic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, trideeanedioic acid, tetradecanedioic acid or octadecanedioic acid.

The branched aliphatic dicarboxylic acid which, together with a diamine, may give the unit Z is, for example, 2,2,4- or 2,4,4-trimethylhexanedioic acid.

The cycloaliphatic dicarboxylic acid which, together with a diamine, may give the unit Z is for example, 1,4-cyclohexanedicarboxylic acid or 1,3-cyclohexanediacetic acid.

To produce the units X, Y and Z a mixture of monomers may be employed in each case in the polycondensation.

Examples of suitable partly aromatic polyamides include:

-   -   the copolyamide of terephthalic acid, hexamethylenediamine and         2-methyl-1,5-pentanediamine;     -   the copolyamide of terephthalic acid, hexamethylenediamine and         the isomer mixture composed of 2,2,4- and         2,4,4-trimethyl-1,6-hexanediamine;     -   the copolyamide of terephthalic acid, isophthalic acid and         hexamethylenediamine (PA6T/6I);     -   the copolyamide of terephthalic acid, hexamethylenediamine and         caprolactam (PA6T/6);     -   the copolyamide of terephthalic acid, adipic acid and         hexamethylenediamine (PA6T/66);     -   the copolyamide of terephthalic acid, isophthalic acid, adipic         acid and hexamethylenediamine (PA6T/6I/66);     -   the copolyamide of terephthalic acid, 1,10-decanediamine or         1,12-dodecanediamine and hexamethylenediamine (PA10T/6T and         PA12T/6T);     -   the copolyamide of terephthalic acid, a linear aliphatic         dicarboxylic acid having 8 to 19 carbon atoms and         hexamethylenediamine (for example PA6T/612) or a linear         aliphatic diamine having 8 to 19 carbon atoms (for example         PA10T/1010);     -   the copolyamide of terephthalic acid or         2,6-naphthalenedicarboxylic acid and an isomer mixture composed         of 1,9-nonanediamine und 2-methyl-1,8-octanediamine;     -   the copolyamide of 1,10-decanediamine or 1,12-dodecanediamine,         terephthalic acid and ω-aminoundecanoic acid(PA10T/11 and         PA12T/11 respectively).

In a preferred embodiment the partly aromatic copolyamide of layer II conforms to the formula of the partly aromatic copolyamide of layer I.

The multilayer composite according to the invention may moreover comprise further layers, for example a further layer I, a further layer II, a layer of a moulding compound based on an aliphatic polyamide, a layer of a moulding compound based on a fluoropolymer or a layer of a moulding compound based on an ethylene-vinyl alcohol copolymer (EVOH).

The multilayer composite according to the invention may be in the form of a flat composite, for example in the form of a sheet or film, for instance in the form of packaging film, or in the form of antiwear tape for flexible pipes for offshore extraction.

In one preferred embodiment the multilayer composite according to the invention is a hollow article, primarily a pipe or a container. This includes, for example, fuel lines, hydraulic lines, brake lines, clutch lines or coolant lines, brake fluid containers or fuel containers. Further applications are, for example, liners for rigid or flexible pipes in the oil or gas extraction industry or lines for umbilicals in which hot liquids are conveyed. When the inner layer is in contact with petrol or biodiesel, it preferably comprises no copper stabilizer.

When the multilayer composite according to the invention is used for conducting or storing flammable liquids, gases or dusts, for example fuel or fuel vapours, it is advisable to impart one of the layers belonging to the composite or an additional inner layer with electrical conductivity. This may be achieved by compounding with an electrically conductive addition according to any related art method. Examples of conductive additions that may be employed include conductive carbon black, metal flakes, metal powder, metallized glass beads, metallized glass fibres, metal fibres (for example of stainless steel), metallized whiskers, carbon fibres (also metallized carbon fibres), intrinsically conductive polymers or graphite fibrils. Mixtures of different conductive additions may also be employed.

The electrically conductive layer is preferably in direct contact with he medium to be conducted or stored and has a specific surface resistance of not more than 10⁹ Ω/square. The measurement method for determining the resistance of multilayer pipes is elucidated in SAE J 2260 of November 2004.

When the multilayer composite according to the invention is implemented as a hollow article or hollow profile (for example a pipe), said composite may further be sheathed in an additional elastomer layer. Both crosslinking rubber compositions and thermoplastic elastomers are suitable for the sheathing. The sheathing may be applied to the multilayer composite either with or without the use of an additional adhesion promoter, for example by extrusion through a crosshead die or by pushing a prefabricated elastomer hose over the previously extruded multilayer pipe. The sheathing generally has a thickness of 0.1 to 4 mm and preferably of 0.2 to 3 mm.

Examples of suitable elastomers include chloroprene rubber, ethylene-propylene rubber (EPM), ethylene-propylene-diene rubber (EPDM), epichlorohydrin rubber (ECO), chlorinated polyethylene, acrylate rubber, chlorosulphonated polyethylene, silicone rubber, Santoprene, polyetheresteramides or polyetheramides.

The multilayer composite may be fabricated in a single-stage or multistage procedure, for example by a single-stage process by means of sandwich moulding, coextrusion, coextrusion blow moulding (also 3D blow moulding, extrusion of a parison into an open half-mould, 3D parison manipulation, suction blow moulding, 3D suction blow moulding, sequential blow moulding for example) or by multistage processes as described in U.S. Pat. No. 5,554,425 for example.

The table which follows lists possible exemplary layer configurations. These examples are intended only for illustration with no intention to restrict the scope of the invention. The cited layer configurations generally apply independently of geometry, i.e. also to films. However, said configurations also apply specifically to hollow articles such as hollow profiles, for example pipes or containers; in this case the layer as per a is the outer layer.

Configuration Layer sequence 1 a) layer I b) layer II 2 a) layer I b) layer II c) layer of a moulding compound based on an aliphatic polyamide 3 a) layer of a moulding compound based on an aliphatic polyamide b) layer II c) layer I 4 a) layer I b) layer II c) layer I 5 a) layer I b) layer of an EVOH moulding compound c) layer I d) layer II 6 a) layer I b) layer II c) layer I (imparted with electrical conductivity) 7 a) layer I b) layer II c) layer of a moulding compound based on an aliphatic polyamide (imparted with electrical conductivity) 8 a) layer I b) layer II c) layer of a fluoropolymer moulding compound modified to impart adhesion 9 a) layer I b) layer II c) layer I d) layer I (imparted with electrical conductivity) 10 a) elastomer layer b) layer I c) layer II d) layer I 11 a) elastomer layer a) layer I c) layer II e) layer II (imparted with electrical conductivity)

It has been found that in the production of the composites according to the invention the moulding compound of layer I and the moulding compound of layer II may be readily coextruded and that an unimpaired layer geometry is obtained. The layer adhesion is also very good. This also applies when the partly aromatic polyamides of layers I and II are different.

The composites according to the invention exhibit a high heat distortion temperature, a very good impact resistance and a high elongation at break. It has moreover been found that only a very small amount of oligomers is washed out of the composite when said composite is in contact with fuel; there are thus no blockages in the fuel supply to the engine. The barrier effect of pipes according to the invention towards fuel components is very good.

Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.

The invention is illustrated by way of example hereinbelow.

EXAMPLES

The following materials were employed in the examples:

PA6T/612: see production example 1

-   -   Colour batch: mixture of 80 wt. % of PA12 and 20 wt. % of carbon         black     -   TAFMER® MH7010: an anhydride-modified ethylene-butylene rubber         from Mitsui Chemicals     -   Calcium stearate: processing aid     -   Polyad® PB201 iodide: copper-containing stabilizer based on         copper iodide and alkali metal halide     -   Naugard® 445: oxidation stabilizer(aromatic amine)     -   HI-PA6T/612 the impact-modified PA6T/612 moulding compound         employed in accordance with the invention     -   Barrier layer moulding     -   Compound: production and composition, see below

PRODUCTION EXAMPLE 1 (PA6T/612 50:50):

A polycondensation vessel was initially charged with 12.621 kg of hexamethylenediamine, 9.021 kg of terephthalic acid, 13.356 ka of dodecanedioic acid, 15.000 kg distilled water and 3.53 g of a 50 weight per cent aqueous solution of hypophosphorous acid. The starting materials were melted at 180° C. and stirred for 3 hours at 225° C./22 bar. The mixture was heated to 300° C. with continuous decompression to 10 bar and then further decompressed at this temperature. Once a pressure of 0.5 bar was obtained the vessel was emptied and the product was pelletized. The granules were subjected to postcondensation in a tumble dryer and thus brought to the desired molecular weight.

Crystallite melting point T_(m): 278° C. (main peak)

Production of the Moulding Compound (HI-PA6T/612) Employed in Accordance with the Invention:

This employed 65.38 parts by wt. of the previously produced PA6T/612, 30 parts by wt. of TAFMER MH7010, 2.5 parts by wt. of colour batch, 1.2 parts by wt, of Polyad PB201 iodide, 0.6 part by wt. of Naugard 445 and 0.32 part by wt. of calcium stearate. The moulding compound was produced from the individual constituents by melt mixing in a kneading unit and then extruded, pelletized and dried.

Production of the Barrier Layer Moulding Compound:

Analogous to the production of HI-PA6T/612 except that, however, TAFMER MH7010, colour batch and Polyad PB201. iodide were omitted.

REFERENCE

An IDE ME 45/4×25D single-layer pipe extrusion apparatus was used to produce single-layer pipes having an outside diameter of 8.0 mm and a wall thickness of 1.0 mm from the moulding composition employed in accordance with the invention, at 280° C. and 100 rpm.

Examples 1 to 3

A Bellaform multilayer pipe apparatus was used to produce multilayer pipes having an outside diameter of 8.0 mm and a total wall thickness of 1.0 mm in each case. The layer configurations are shown in Table 1.

Tests:

-   -   a) Tensile test: The single- and multilayer pipes were tested in         accordance with DIN EN ISO 527-1 at a takeoff speed of 100         mm/min. The test specimens had a length of about 200 mm, the         clamped length was 100 mm and strain sensor spacing was 50 mm.     -   b) Impact bending test: Measurement of impact resistance for the         single- and multilayer pipes was performed in accordance with         DIN 73378 at 23° C. and −40° C. Ten pipe sections of about 100         mm in length were used in each case,     -   c) Fall hammer test: The fall hammer test was carried out as per         SAE specifications. This comprised allowing a specific weight to         fall onto the test specimen from a prescribed fall height. This         test was used to determine the impact resistance characteristics         under the effect of an impact of the single- and multilayer         pipes according to SAE J2260 and SAE J844. In each case ten test         specimens were measured at −40° C. and, once subjected to the         test, visually inspected for damage.     -   d) Separation test: The separation test was carried out with a         Zwick BZ 2,5/TN1S tensile tester to which a tensile device and a         rotating metal wheel are attached to enable the individual         layers of the test sample to be separated from one another, The         separation test in accordance with DIN EN ISO 2411 was used to         determine the adhesion between two layers by measuring the force         required to separate the two layers from one another. To this         end, pipe sections of the multilayer pipes 20 cm in length were         divided longitudinally into three portions using a cutting         device.

Prior to starting measurement, calipers were used to measure the sample width repeatedly at different points and the average value was entered into the evaluation software, The incipiently separated end of one layer was then held in a clamp which continuously pulled said layer from the second layer at an angle of 90°.

The layers were pulled apart at a test speed of 50 mm/min while, simultaneously, a diagram of the required force in newtons versus the displacement in millimetres was recorded. This diagram was used to determine the separation resistance in newtons per millimetre which relates to the width of the adherent contact area.

The results are shown in Table 1.

Oligomer Washout Stability:

The oligomer washout stability tested the mass of soluble and insoluble extract washed out from a pipe per meter thereof by a test fuel. This test comprised storing the alcohol-containing test fuel FAM B (42.3 vol % of toluene, 25.4 vol % of isooctane, 4.3 vol % of ethanol, 12.7 vol % of diisobutylene, 15.0 vol % of methanol and 0.5 vol % of deionized water) in pipe sections of two metres length for 72 hours at 60° C. One end of each pipe was sealed with a metal ball for sample preparation, The specimens were filled to about 95% full with the test fuel and sealed and then placed in a circulating air oven at 60° C., Once the test time of 72 hours had elapsed the pipes were removed, cooled to room temperature and briefly shaken to dissolve any residues on the pipe inner wall, Each test liquid was transferred into a. glass beaker, cooled to 0° C. and stored at this temperature for a further 24 hours. The insoluble extract comprised in the test liquid was filtered off under suction using a polyethersulfone (PES) filter having a 0.045 μm pore size and then weighed. The filtrate was then evaporated for 24 hours in a fume hood and the residue was weighed. A triple determination was carried out in each case.

The pipe from example 1 afforded 1.4 mg/m of pipe of insoluble extract and 88 mg/m of pipe of residue after evaporation of the filtrate.

For comparison: after the same procedure a single layer pipe made of the PA12 moulding compound VESTAMID® X7293, which is often used as the inner layer in multilayer pipes, yielded 15.9 mg/m of pipe of insoluble extract and 853 mg/m of pipe of residue after evaporation of the filtrate.

TABLE 1 Layer configurations and test results Reference Example 1 Example 2 Example 3 outer layer HI- HI- HI-PA6T/612; HI-PA6T/612; 0 8 mm PA6T/612, PA6T/612; 0.35 mm 1.0 mm 0.4 mm interlayer — barrier layer barrier layer — moulding moulding compound; compound; 0.3 mm 0.2 mm inner layer — HI- HI-PA6T/612; barrier layer moulding PA6T/612; 0.35 mm compound; 0.2 mm 0.4 mm adhesion [N/mm] outer layer to outer layer to outer layer to inner layer: interlayer: interlayer: separation not possible separation separation not not possible possible interlayer to interlayer to inner layer: inner layer: separation separation not not possible possible modulus of 1121 1160 1380 1190 elasticity [MPa] tensile stress at 44 45.1 46.1 45.3 break [MPa] elongation at break 480 435 381 411 [%] impact no fracture no fracture no fracture no fracture resistance 23° C.-40° C. no fracture no fracture no fracture no fracture fall hammer test no fracture no fracture no fracture no fracture SAE J2260, −40° C.

The pipes according to the invention thus meet the requirements imposed on fuel lines.

European patent application EP15159399 filed Mar. 17, 2015, is incorporated herein by reference.

Numerous modifications and variations on the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 

1. A multilayer composite, comprising the following layers:
 1. a first layer (layer I) of a moulding compound comprising at least 40 wt. % of the following components: 1) 60 to 95 parts by wt. of a partially aromatic copolyamide which contains monomer units which are obtained from α) 30 to 90 mol % of a combination of hexamethylenediamine and terephthalic acid, and β) 70 to 10 mol % of a combination of hexamethylenediamine and a linear aliphatic dicarboxylic acid having 8 to 19 carbon atoms; wherein the mol % values relate to the sum of α) and β), and wherein not more than 20% of the hexamethylenediamine is optionally replaced by the equivalent amount of another diamine, and/or wherein not more than 20% of the terephthalic acid is optionally replaced by the equivalent amount of another aromatic dicarboxylic acid and/or 1,4-cyclohexanedicarboxylic acid, and/or wherein not more than 20% of the repeating units containing hexamethylenediamine and linear aliphatic dicarboxylic acid is optionally replaced by the equivalent quantity of units obtained from a lactam/an ω-aminocarboxylic acid having 6 to 12 carbon atoms, 2) 40 to 5 parts by wt. of an olefinic copolymer as impact modifier, wherein the parts by wt. of 1) and 2) sum to 100; and II. a second layer (layer II) of a moulding compound comprising at least 60 wt. % of a mixture of the following components: 1) 75 to 100 parts by wt. of a partly aromatic copolyamide, and 2) 25 to 0 parts by wt. of an olefinic copolymer as impact modifier with the proviso that in the moulding compound of layer II the mixture of components 1) and 2) comprises at least 5 fewer parts by wt, of olefinic copolymer than in the moulding compound of layer I.
 2. The multilayer composite according to claim 1, wherein the moulding compound of layer I comprises 0.01 to 60 wt. % of at least one further additive.
 3. The multilayer composite according to claim 2, wherein one of the further additives is a copper-containing stabilizer.
 4. The multilayer composite according to claim 2, wherein one of the further additives is an oxidation stabilizer.
 5. The multilayer composite according to claim 1, wherein the crystallite melting point T_(m) of the copolyamide of layer I is in the range from 220° C. to 300° C. when measured as per ISO 11357 at 2nd heating.
 6. The multilayer composite according to claim 1, wherein the partly aromatic polyamide of layer II has the composition PAXY/Z, wherein the individual units have the following meanings: X is a unit obtained from an aromatic dicarboxylic acid; Y is a unit obtained from a diamine; Z is either a unit obtained from a lactam or an w-aminocarboxylic acid, or a unit obtained from the combination of a linear aliphatic, branched aliphatic or cycloaliphatic dicarboxylic acid and a linear aliphatic, branched aliphatic or cycloaliphatic diamine, wherein the proportion of Z based on the sum of X, Y and Z is 0 to 60 mol %.
 7. The multilayer composite according to claim 1, which comprises one or more further layers.
 8. The multilayer composite according to claim 7, wherein the further layer or the further layers are selected from the group consisting of: a further layer I, a further layer II, a layer of a moulding compound based on an aliphatic polyamide, a layer of a moulding compound based on a fluoropolymer, a layer of an EVOH moulding compound, and combinations thereof.
 9. The multilayer composite according to claim 1, which is a film, a sheet or a hollow article.
 10. The multilayer composite according to claim 9, which is a hollow article and wherein the hollow article is a hollow profile.
 11. The multilayer composite according to claim 10, which comprises one or more further layers selected from the group consisting of an electrically conductive layer, an elastomer sheathing and combinations thereof.
 12. The multilayer composite according to claim 10, wherein said composite is a fuel line, a hydraulic line, a brake line, a clutch line, a coolant line, a liner for rigid or flexible pipes in the oil or gas extraction industry or a line for an umbilical.
 13. The multilayer composite according to claim 10, wherein said composite is a brake fluid container or a fuel container.
 14. The multilayer composite according to claim 10, wherein the hollow profile is a pipe, or a container. 